1. Field of the Invention
The present invention relates to a centrifugal master clutch and a vehicular transmission system utilizing the same. In particular, the present invention relates to an automated vehicular transmission system comprising an engine, a multiple ratio transmission, a centrifugally operated master friction clutch for drivingly coupling the engine to the transmission and a controller for controlling fueling of the engine during vehicle launch conditions, as a function of throttle position and other sensed system operating conditions such as at least one of engine speed, transmission input shaft speed, transmission output shaft speed, engine torque and engaged gear ratio.
More particularly, an exemplary embodiment of the present invention relates to a start control method/system for a vehicular automated mechanical transmission system utilizing a centrifugal master friction clutch controlled solely by engine speed and a controller for controlling engine fueling during vehicle launch conditions.
2. Description of the Prior Art
Automated mechanical transmission systems not requiring the vehicle driver or operator to operate the vehicle master clutch (so called xe2x80x9ctwo-pedal systemsxe2x80x9d), and clutch controls and actuators therefore, are known in the prior art as may be seen by reference to U.S. Pat. Nos. 4,081,065; 4,361,060; 4,936,428; 5,439,428; 5,634,867; 5,630,773; 5,960,916 and; 5,947,847, the disclosures of which are incorporated herein by reference. These systems are not totally satisfactory as separate clutch actuators, sensors and/or, electrical and/or fluid power (i.e., compressed and/or hydraulic) connections thereto are required which adds to the expense of providing, assembling and maintaining such systems.
Centrifugally operated friction clutches are well known in the prior art and typically include a driving input member driven by a prime mover, usually an electric motor or internal combustion engine, and weights rotatable with the driving member which, upon rotation of the driving member, will move radially outwardly under the effect of centrifugal force to cause the driving input member to frictionally engage a driven output member. Examples of centrifugally operated clutches may be seen by reference to U.S. Pat. Nos. 3,580,372; 3,696,901; 5,437,356; 3,810,533; 4,819,779; 5,441,137; 5,730,269; and; 4,610,343, the disclosures of which are incorporated herein by reference.
Fully or partially automated mechanical transmission systems that, upon determining that a dynamic shift from a currently engaged ratio into neutral and then into a target ratio is desirable, will, while maintaining the vehicle master friction clutch engaged, initiate automatic fuel control to cause reduced torque across the jaw clutches to be disengaged, are known in the prior art as may be seen by reference to U.S. Pat. Nos. 4,850,236; 5,820,104; 5,582,558; 5,735,771; 5,775,639; 6,015,366; and 6,126,570, the disclosures of which are incorporated herein by reference. These systems include systems that attempt to fuel the engine to achieve a sustained zero driveline torque, and systems which force torque reversals, see U.S. Pat. No. 4,850,236. These systems, upon sensing a neutral condition, will, while maintaining the master clutch engaged, cause the engine to rotate at a speed determined to cause synchronous conditions for engaging the target ratio.
Vehicular driveline systems, especially for heavy-duty vehicles, utilizing centrifugal clutches have not been satisfactory as the engines were typically controlled by throttle device position, not on a closed loop basis based upon a target engine speed and/or engine torque, and thus did not provide acceptable control for smooth vehicle launch.
Centrifugal clutches are in significant part mechanical in nature. As such, each clutch will vary slightly in its dynamic characteristics from others of the same design. Performance differences will also occur over time with an individual clutch with use of the clutch as parts wear and get dirty. Such variation can potentially result in engagement characteristics, such as clamping load at a particular engine speed varying over time and from clutch to clutch.
Centrifugal clutch engagement is controlled by varying the speed of the engine. A sudden increase in throttle position, and a corresponding increase in engine speed, will result in a sudden engagement of the centrifugal clutch. It is desired to avoid harsh engagements so as not to subject the driveline to harsh impact loads.
It is also desired to increase the engine torque at clutch lock-up in high-demand situations so as to prevent excessive slipping.
In accordance with the present invention, the drawbacks of the prior art are reduced or minimized by the provision of a centrifugal master friction clutch, and a vehicular automated transmission system utilizing the same, which utilizes closed loop control to modulate clutch engagement by using the controller to limit the engine speed.
A method for controlling a vehicular automated transmission system to modulate engagement of a centrifugal clutch is disclosed herein. The automated transmission system includes an internal combustion engine having an engine output member, a multiple speed change gear transmission having an input shaft, the centrifugal friction clutch for drivingly connecting the engine output member to the input shaft, and a throttle responsive to manually requesting of a degree of engine fueling. The system controller receives input signals including two or more of signals of (i) engine speed, (ii) input shaft speed, (iii) throttle position, (iv) vehicle speed, and (v) engaged transmission ratio. The system controller has at least one mode of operation for selectively controlling engine fueling to control at least one of engine speed and engine torque. The system controller processes the signals according to logic rules to issue command output signals to system actuators including at least the engine controller. The method includes the steps of:
a) establishing a curve of an engine speed limit as a function of a throttle position and storing the curve within the system controller;
b) sensing the throttle position;
c) establishing a target engine speed limit for the sensed throttle position using the stored curve;
d) sensing the engaged transmission ratio;
e) after sensing engagement of a drive transmission ratio, automatically increasing the engine speed under control of a vehicle-start-from-rest routine until the target engine speed limit is reached; and
f) after sensing that the clutch is engaged, releasing control of the engine speed by the vehicle-start-from-rest routine, with the centrifugal friction clutch drivingly connecting the engine output member to the input shaft.
A method for controlling a vehicular automated transmission system to modulate engagement of a centrifugal clutch is disclosed herein. The automated transmission system includes an internal combustion engine having an engine output member, a multiple speed change gear transmission having an input shaft, the centrifugal friction clutch for drivingly connecting the engine output member to the input shaft, and a throttle responsive to manually requesting of a degree of engine fueling. The system controller receives input signals including two or more of signals of (i) engine speed, (ii) input shaft speed, (iii) throttle position, (iv) vehicle speed, and (v) engaged transmission ratio. The system controller has at least one mode of operation for selectively controlling engine fueling to control at least one of engine speed and engine torque. The system controller processes the signals according to logic rules to issue command output signals to system actuators including at least the engine controller. The method includes the steps of:
a) sensing input shaft rotation;
b) upon sensing an initiation of input shaft rotation, recording a touch point speed equal to the engine speed at the initiation of input shaft rotation.
c) establishing a curve of an engine speed limit as a function of a throttle position and the touch point speed and storing the curve within the system controller;
d) sensing the throttle position;
e) establishing a target engine speed limit for the sensed throttle position using the stored curve;
f) sensing the engaged transmission ratio;
g) after sensing engagement of a drive transmission ratio, automatically increasing the engine speed under control of a vehicle-start-from-rest routine until the target engine speed limit is reached; and
h) after sensing that the clutch is engaged, releasing control of the engine speed by the vehicle-start-from-rest routine with the centrifugal friction clutch drivingly connecting the engine output member to the input shaft.
A control system for controlling a vehicular automated transmission system to modulate engagement of a centrifugal clutch is disclosed herein. The automated transmission system includes an internal combustion engine having an engine output member, a multiple speed change gear transmission having an input shaft, the centrifugal friction clutch for drivingly connecting the engine output member to the input shaft, and a throttle responsive to manually requesting of a degree of engine fueling. The system controller receives input signals including two or more of signals of (i) engine speed, (ii) input shaft speed, (iii) throttle position, (iv) vehicle speed, and (v) engaged transmission ratio. The system controller has at least one mode of operation for selectively controlling engine fueling to control at least one of engine speed and engine torque. The system controller processes the signals according to logic rules to issue command output signals to system actuators including at least the engine controller. The controller is characterized by the system controller having logic rules effective for:
a) establishing a curve of an engine speed limit as a function of a throttle position and storing the curve within the system controller;
b) sensing the throttle position;
c) establishing a target engine speed limit for the sensed throttle position using the stored curve;
d) sensing the engaged transmission ratio;
e) after sensing engagement of a drive transmission ratio, automatically increasing the engine speed under control of a vehicle-start-from-rest routine until the target engine speed limit is reached; and
f) after sensing that the clutch is engaged, releasing control of the engine speed by the vehicle-start-from-rest routine, with the centrifugal friction clutch drivingly connecting the engine output member to the input shaft.
The invention advantageously provides a driveline system utilizing a centrifugal clutch with acceptable control for a smooth vehicle launch.
The invention advantageously compensates for variation in engagement characteristics which occur over time.
The invention controls clutch engagement to avoid harsh engagements.
The invention increases torque at clutch lock-up in high demand situations to prevent excessive slipping.
The invention limits engine speed to prevent harsh loading of the driveline.
The engine speed is limited as a function of throttle position so as to increase the available torque capacity for higher throttle applications likely to be associated with high-demand circumstances while still avoiding harsh loading.
The engine speed limit employs a dual slope line to further optimize clutch engagement for varying throttle applications.
The target speed limit is shifted with the engine speed at which clutch engagement is initiated to compensate for variations in the system. As the speed at which engagement is initiated increases or decreases, the speed limit curve is raised or lowered.
These and other objects and advantages of the present invention will become apparent from a reading of the following description of the preferred embodiment taken in connection with the attached drawings.